1. Field of the Invention
The present invention relates to a structure of a pin bore of a piston for use in an engine.
2. Description of the Related Art
Conventionally, a piston pin for connecting a connecting rod is assembled to a piston used in an engine, and axial ends of the piston pin are supported to pin bores formed coaxially with each other in a pair of piston pin supporting portions of the piston.
In a piston as described above, as described in Japanese Utility Model Unexamined Publication No. Hei.3-42046, a lubricating oil holding portion is provided by forming an axial groove in an inner circumferential surface of a pin bore (for a piston pin) along an axial direction thereof. In addition, a piston pin is normally prevented from being removed by mounting a snap ring which is an annular ring in a snap ring groove formed in an inner circumferential surface of a pin bore. In servicing a vehicle for maintenance, there is a need for the piston pin to be removed, and in order to facilitate the removal thereof, there is formed a snap ring groove relief as a recessed portion for a relevant tool to be inserted thereinto for removing the snap ring.
However, the recessed portion is formed deeper than the axial groove from a need for the tool to be inserted thereinto. This causes a problem that the rigidity of the piston pin supporting portion is deteriorated at the recessed portion.